In recent years, a side airbag that protects a head portion of a passenger when the vehicle collides is installed at the side of a seatback or inside roof above doors of vehicle. This side airbag apparatus has an inflator that generates an expansion gas after the vehicle collides and receives a large impact, and an airbag that is expanded by inflation when the gas is supplied from the inflator. In a state that the airbag is accommodated before the side airbag apparatus works, the airbag is accommodated at the side of the seatback of the vehicle seat, for example, by being folded in a predetermined procedure, and the side airbag apparatus itself is covered by a seat cover and the like.
Usually, a seat cover such as a fabric and a leather to cover a cushion member of a seat is covered on a front surface of a vehicle seat. An expansion opening for expanding the airbag is formed in the seat cover at the side of the seatback where the side airbag apparatus is installed. Conventionally, this expansion opening is sewed by a fragile sewing thread that is disconnected when the expansion opening is pulled with predetermined force.
When a vehicle collides and receives a large impact, this side airbag apparatus senses this impact, generates a high-pressure gas from the inflator, introduces the gas into the airbag, and momentarily expands the airbag. When the airbag is expanded, excessively large tensile force is applied to the sewing thread that is used to sew the expansion opening. Therefore, the sewing thread is disconnected by this tensile force, and the expansion opening so far closed is opened and the airbag is expanded from this opening. This airbag is expanded to the side of a passenger, and supports the head portion, the breast portion, and the lumber portion of the passenger by buffering. With this arrangement, impact strength applied to a human body at a collision time can be substantially alleviated, and safety of the passenger can be secured.
However, when a structure to close the expansion opening of the airbag with the sewing thread is employed, a seat cover needs to be covered on the seat after the airbag apparatus is installed on the seat, and this generates inconvenience that a manufacturing process is limited. Many recent vehicle seats are installed with various auxiliary apparatuses such as a heater and an actuator for adjusting a seat height, and a degree of freedom in the manufacturing process is desired. Further, conventionally, when inspection of the airbag apparatus is necessary after delivery of a vehicle, the airbag apparatus cannot be inspected without removing the seat cover, and this makes a work process complex.
Further, there is inconvenience that rupture strength of a sewing thread greatly changes depending on a sewing state, and also greatly changes depending on a temperature increase in a vehicle chamber and ageing. When the sewing thread is not easily disconnected, serious inconvenience occurs that the airbag does not expand at an emergency time. When strength of the sewing thread is small, and also when strong tensile force works on the seat cover when a passenger is seated, the sewing thread is ruptured, the expansion opening is cleaved, and the seat cushion is exposed.
When the airbag is expanded, each sewing thread is sequentially ruptured. Therefore, an expansion speed of the airbag decreases.
In place of the structure of closing the expansion opening by using a sewing thread having various kinds of inconvenience as described above, a closing structure of the expansion opening that uses a slide fastener is calling attention. The slide fastener can freely open and close the expansion opening by sliding a slider even after the slide fastener is sewed to the seat cover. Therefore, a seat having a complex structure can be easily assembled by increasing a degree of freedom of the assembling process. When inspecting the airbag apparatus, wiring and an attaching portion can be easily inspected by opening and closing the slide fastener.
When a coupling between elements is disengaged at a part of the slide fastener where the elements are coupled, and when lateral pulling force is continuously applied in this state, a coupling between elements of rows of elements can be disengaged with weak force without moving the slide fastener, starting from a portion where the coupling is disengaged. Therefore, a cleave speed becomes fast, unlike a speed when sewing threads are sequentially ruptured. Consequently, development of expansion of the airbag can be performed quickly, and a passenger can be effectively protected. Particularly, because a distance between a head portion of a passenger and a side glass of a vehicle is configured small, the side airbag needs to be expanded in a short time after a collision.
Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-15158), for example, discloses a slide fastener that has an emergency opening unit having an easy cleave structure to be used for an expansion opening of an airbag.
The slide fastener having an emergency opening unit disclosed in Patent Document 1 uses an insert-molding method for fixing elements to an element-attached portion of a fastener tape simultaneously with formation of the elements. Each element of the slide fastener has two leg portions that are fixed to stride the element-attached portion of an edge portion of the fastener tape, a body portion that connects the two leg portions, a coupling head portion that is formed at an external end portion to couple a pair of elements at left and right sides in a lateral pulling direction, and a neck portion that connects between the coupling head portion and the body portion. A trench is formed along a coupling axis line at a crest portion of the coupling head portion. A shoulder portion to be engaged with the trench is formed to bulge from the body portion and the neck portion at a center portion of the elements in a width direction.
The coupling head portions are engaged with neck portions of two adjacent elements fixed to the other fastener tape of oppositely arranged fastener tapes, to prevent cleavage of the coupled elements in a lateral pulling direction, by lateral pulling force equal to or smaller than predetermined cleavage lateral pulling force that cleaves the coupled state of the elements. The shoulder portion that is formed to bulge is configured to be engaged with the trench provided in the opposite coupling head portion. Therefore, the shoulder portion prevents disengagement of left and right fastener stringers by being deviated to a shearing direction.
Further, according to the slide fastener described in Patent Document 1, back-surface sides of the coupling head portions engaged with the shoulder portions of the elements are disconnected. Therefore, two elements having front-and-back asymmetrical coupling head portions are arranged at the center portion of the slide fastener. This portion is easily cleaved with force pushed up from the back-surface side of the slide fastener, and becomes a cleavage start point of the slide fastener when expanding the airbag.